ESTRO 37 Abstract book

S871

ESTRO 37

7 University of Newcastle, School of Mathematical and Physical Sciences, Newcastle, Australia 8 Royal Brisbane Hospital, Australian e-Health Research Centre- CSIRO, Herston, Australia 9 Calvary Mater Newcastle Hospital, Radiation Oncology, Newcastle, Australia Purpose or Objective Prostate cancer toxicity studies often have smaller pelvic structures contoured by a single expert clinician. Presently limited information is available regarding variability of clinician contouring of these structures. This study sought to document inter-observer contouring variation for a range of pelvic structures on both CT and MR. Material and Methods Five patient datasets, each incorporating CT and T2- weighted MR scans, were circulated to 13 volunteers for contouring. Guidelines and a sample patient dataset with expert defined contours were also distributed. Volunteers consisted of radiation oncologists, radiotherapists, and medical physicists, each covering a range of clinical experience. Structures to be contoured on CT were CTV (prostate), seminal vesicles, rectum, distal colon, bowel bag, bladder, and peri-rectal space. T2-MR structures included CTV, trigone, membranous urethra, penile bulb, neurovascular bundle (left and right), and multiple pelvic floor muscles (internal anal sphincter, external anal sphincter, puborectalis muscle, and levator ani muscles). Post processing of bowel bag contours required subtraction of bladder, CTV, and seminal vesicles outlines. Contouring variations were calculated by pairwise analysis using DSC, volume similarity, Hausdorff distance, mean absolute surface distance, sensitivity, specificity, and centroid distances. Results Spread in contoured volumes are shown in figure 1, where volumes have been normalised with respect to the median structure volume for each patient. Pairwise analysis of DSC between observer contours are shown in figure 2. Mean DSC for CTV (CT: 0.83, MR: 0.88), bladder (0.93), and rectum (0.81) were comparable to values observed in the literature. Distal colon and bowel bag contours recorded poor overlap, however minimal volume spread suggest that slice selection, dependent on the superior slice contoured for rectum, was the most significant factor for contouring variation for these structures. Variations in volume and DSC were more substantial for MR structures. Multiple neurovascular contours had minimal to no overlap. Average Hausdorff and mean absolute surface distance for CT structures (17.669 mm, 3.342 mm respectively) were comparable to MR structures (13.275 mm, 3.954 mm), suggesting that localisation of the structure, as opposed to identification of the structure’s boundary, was the largest contribution to variations in observer’s MR contours.

volume for each patient. Outlier volumes for neurovascular bundle (ranging from 4 – 7) were omitted for clarity.

Figure 2: Pairwise DSC analysis between observers across all patients.

Conclusion Significant variation in observer contouring for MR pelvic structures was observed. Studies incorporating these structures should assess the accuracy and reproducibility of observer contours before proceeding with investi- gations.

Electronic Poster: Clinical track: Urology-non-prostate

EP-1615 Tri-modalities for bladder cancer in elderly: TUR, hypofractionated radiotherapy and gemcitabine H. Hamza Abbas 1 , M. Salem 2 , A. Gbre 3 , M. Engaar 4 1 South Egypt Cancer Institute - Assiut Unversity, RADIATION ONCOLOGY, Assiut, Egypt 2 South Egypt Cancer institute assiut unvesity, Surgical Oncology, Assiut, Egypt 3 South Egypt Cancer institute, medical oncology, Assiut, Egypt 4 faculty of medicine assiut unversity, clinical oncology, Assiut, Egypt Purpose or Objective A prospective phase II study carried to evaluate hypofractionated radiotherapy with concurrent gemcitabine for bladder preservation in elderly. Material and Methods Thirty-one patients enrolled, their age ≥ 65 years, diagnosed transitional cell carcinoma (TCC) of the urinary bladder with clinical stage T2 or T3, N0, M0, after maximum safe transurethral resection of the bladder tumour. They received 52.5 Gy in 20 fractions using 3DCRT with concurrent gemcitabine 100 mg/m2 weekly as a radio-sensitizer Results All patient completed their radiation therapy course, while seven patients received their chemotherapy irregularly due to G 3 toxicities. Twenty-five patients (80.6%) achieved a complete response. At 2-years, OAS is 94.4% and DFS is 72.6%. T3 and residual after TUR are factors that adversely affects DFS. Conclusion Hypofractionated radiotherapy and gemcitabine as a radiosensitizer in elderly as organ preservation for TCC bladder cancer have acceptable toxicity profile with good response rate and disease-free survival, keeping salvage cystectomy for persistence or recurrence of invasive cancer.

Figure 1: Contoured volume variation for CT (blue) and MR (green) structures, normalised to median structure